The recent development of high-rate cathodic sputtering, such as those obtained using magnetic fields (magnetically enhanced sputtering), is presently providing a major contribution to the coating field, and renders possible the production of coatings on an industrial scale for many applications.
The major problem of optimal consumption of the sputtering target, and the requirement of an essentially continuous production in industrial manufacturing gives rise to a fast consumption of the sputtering target as the consumption proceeds to the piercing of the target, which may cause irremediable damage in all known high-rate sputtering systems.
All known high-rate sputtering systems are designed to ensure proper target cooling which is rendered indispensible because of the high power dissipation and have either of these two basic designs:
"direct cooling" arrangement where the liquid coolant is circulated directly along the back of the sputtering target, in which case the target piercing causes some irremediable damage inside the vacuum bell jar by flooding it with the coolant (there is also a risk of premature target piercing because of the high differential pressure directly exerted by the coolant on the target), and,
"indirect cooling" arrangement where the liquid coolant is circulated along an intermediate support against which the target is mounted (the target being in contact with the intermediate support, or bonded to it by any suitable means), in which case the target piercing would cause the sputtering of the intermediate support instead of the target, causing irremediable damaging of the substrate; notwithstanding the other drawbacks of an intermediate support, such as high manufacturing costs of a target to be bonded against the intermediate support, or lack of a good thermal contact (likely to be aggravated by thermal dilation) of a target to be maintained in contact against the intermediate support.
Since the exact instant of target piercing is unforeseeable, the only solution for avoiding irremediable damage to the apparatus or the coated substrates requires coupling the partially consumed sputtering target wall before its piercing, resulting in more frequent interruptions in the manufacturing process, and significant material losses. These losses are enhanced when the target material is very rare or when the target material is difficult to work into the desired shape.